WINNIPEG - A transport official says a mid-air collision that killed five people in Saskatchewan occurred when the left wings of the two small planes came into contact.

Wreckage from the Piper PA-28 and Lake Buccaneer amphibious plane includes marks that show the wings of the single-engine aircraft touched before the planes plummeted almost straight down, Peter Hildebrand of the Transportation Safety Board said Tuesday.

"The wreckage came down almost vertically in its final trajectory," said Hildebrand, who added that there was no way anyone could have survived the impact.

The crash occurred Saturday near St. Brieux northeast of Saskatoon. The Piper's three occupants — two men and an 11-year-old boy — were from rural Alberta. A Regina couple were in the Buccaneer.

Despite good weather, it may have been difficult for the pilots to judge each other's speed and distance, because they were likely at 90-degree angles to each other, Hildebrand said. Flight plans suggest the Piper would have been heading east while the Lake Buccaneer was heading north toward La Ronge.

"It may be difficult to see other aircraft, depending on your angle, depending on the structure of aircraft components and other background visual information the pilots might be seeing," Hildebrand said.

"If aircraft approach head-on, for example, then there's no relative movement that's apparent to you in the windshield if you're looking out as a pilot. If aircraft approach at a 90-degree angle, that's another scenario where it's difficult to see because ... the angle stays the same and you don't have relative movement across the windshield."

Hildebrand cautioned that the investigation is in its early stages and is facing challenges. The wreckage is scattered over a wide area and some of it is submerged in a marsh.

Investigators still want to recover flight instruments or electronic equipment that could assist in the investigation. They would also like to interview anyone who may have seen what happened.

Police have not yet released the names of the five people killed, but family members say the three on board the Piper were Denny Loree, Eric Donovan and his 11-year-old son, Wade — all from Mossleigh, Alta. They were on their way to St. Brieux to pick up farm equipment, according to a cousin.

An obituary in a Saskatchewan newspaper said Joy and Eric Jackson of Regina were the other two people killed in the crash.

Hildebrand said mid-air collisions are rare in Canada. There had been only 16 in the last 10 years before Saturday.